The present invention generally relates to a method and apparatus for heat transfer with a patient, and more particularly to a method and apparatus for cooling and/or heating a localized tissue region of interest on a patient.
The use of heating/cooling devices in medial applications is well established. By way of example, bodily heating may be employed for hypothermia patients. Hypothermia may occur, for example, in patients undergoing surgical procedures. It has been shown that nearly seventy five percent of all patients who undergo surgical procedures develop hypothermia from factors including anesthesia, air conditioning of the operating room, and infusion of cold blood or I-V solutions. Studies show that by reducing hypothermia, patient outcome is improved and recovery is quicker.
Further, bodily cooling has been proposed for stroke patients to reduce potential brain damage due to ischemia. In this regard, studies show that cooling the brain 2-3xc2x0 C. yields neuro-protection that might hasten recovery. Additionally, during vascular procedures requiring circulatory arrest, a common technique is to cool the patient""s core via cardiovascular extracorporeal perfusion to less than 15xc2x0 C. In order to maximize protection of major organs, including the brain and spine, peripheral cooling may be employed to prevent rewarming via heat conduction from surrounding tissues.
To date, self-contained thermal exchange pads and other devices have been used for cooling and/or heating of a patient. Fluids, such as water, are circulated between layers of the thermal exchange pad to cool or heat the patient. For example, fluids colder/hotter than the patient""s body temperature may be circulated through the pad to absorb/release heat from/to the patient, thereby achieving cooling/heating. While such devices have proven effective for many applications, the present inventor has recognized that further improved results are achievable in certain applications.
Accordingly the present invention provides a method and apparatus for enhanced heat transfer with a localized tissue region of interest. The apparatus/method utilizes a membrane configured for covering a tissue region of interest and a spacing structure that maintains a spacing relation between an interior side of the flexible membrane and the tissue region of interest to define a fluid circulation space therebetween. Thermal exchange fluid may be drawn into the fluid circulation space through an inlet in the flexible membrane and out of the fluid circulation space through an outlet in the flexible membrane. In this regard, the fluid directly contacts the tissue region of interest. A related fluid circulation system includes a pump connected downstream from the fluid outlet and a fluid reservoir connected upstream from the fluid inlet. When operated, the pump draws thermal exchange fluid from the reservoir, into, and out of the fluid circulation space. Thermal energy is exchangeable between the tissue region of interest and the thermal exchange fluid circulated within the fluid circulation space to cool and/or warm the tissue region of interest.
The fluid may be circulated under negative or nearly negative gauge pressure which has several advantages. For example, the flexible membrane is not distended/expanded by the pressure of the circulated fluid and thereby fluid velocity over the tissue region of interest is maximized thus maximizing heat transfer. Circulating the fluid under negative or nearly negative gauge pressure also achieves inherent sealing at the edges of the flexible membrane as compared to a positive pressure situation. Further, direct contact of the fluid with the tissue region of interest also enhances heat transfer where the tissue region of interest is covered by hair (e.g. a person""s head) as compared with a thermal exchange pad which contains the fluid and prevents direct contact of the fluid with the tissue region of interest.
According to one aspect of the present invention, an apparatus for local exchange of thermal energy with a tissue region of interest includes a flexible membrane having an interior side and an exterior side. The flexible membrane is configured for covering the tissue region of interest. The flexible membrane may be comprised of an elastic material, such as silicone rubber, natural rubber, an elastomer, a thermoplastic polyurethane or a latex material, to allow for stretching of the flexible membrane to facilitate positioning of the flexible membrane over a body element (e.g., over a patient""s head). The apparatus also includes a spacing structure for maintaining the interior side of the flexible membrane in a spaced relation with the tissue region of interest to define a fluid circulation space therebetween. The apparatus further includes at least one fluid inlet and at least one fluid outlet communicating with the fluid circulation space. A thermal exchange fluid is circulatable through the fluid circulation space from the inlet to the outlet at or near a negative gauge pressure (i.e. pressure measured relative to ambient pressure). In this regard, the thermal exchange fluid may be circulated through the fluid circulation space at a gauge pressure ranging from slightly positive (e.g., about 0.1 psi) to substantially negative (e.g., about xe2x88x9210.0 psi).
The spacing structure may be comprised of one or more ribs, one or more studs, or a combination of both. The spacing structure may be integrally molded to the interior side of the flexible membrane and project from the interior side of the flexible membrane. However, the spacing structure may also be removably attached to the interior side of the flexible membrane or may even be a separate structure such as a net or the like that is disposable between the tissue region of interest and the interior side of the flexible membrane. The spacing structure may define a plurality of fluid flow paths from the fluid inlet to the fluid outlet. In this regard, the fluid flow paths are generally of equal length from the fluid inlet to the fluid outlet and inhibit the formation of boundary layers of stationary thermal exchange fluid that may reduce the overall efficiency of the apparatus.
The flexible membrane may also include a sealable edge. In one embodiment the sealable edge may comprise a strip, located on the periphery of the interior side of the flexible membrane that is free of any spacing structure (e.g. smooth). In another embodiment, the strip may include a plurality of elongated parallel ridges projecting from an interior side of the strip. In use, the ridges are forced into the periphery of the tissue region of interest such that portions between the ridges are approximately coplanar with the tissue region of interest. In another embodiment, the sealable edge may include an adhesive material disposed on the interior side of the strip. The adhesive aids in facilitating a tight seal between the sealable edge and the periphery of the tissue region of interest. In this regard, the adhesive on the seal should be comprised of a material having sufficient adhesive strength for holding the flexible membrane in place without having too great of an adhesive strength so as to cause tissue damage during removal. Generally, for best results, the sealable edge should be positioned next to a portion of the patient""s skin that lacks substantial hair. The above-described embodiments of the sealable edge allow the sealable edge to grip the patient""s skin, and thus help maintain the conformance of the flexible membrane to the tissue region of interest to limit unintentional movement of the flexible membrane.
According to another aspect of the present invention, a system for local exchange of thermal energy with a tissue region of interest includes a flexible membrane configured for covering the tissue region of interest and a spacing structure that maintains an interior side of the flexible membrane in a spaced relation with the tissue region of interest to define a fluid circulation space therebetween. The system further includes one or more fluid inlets and fluid outlets communicating with the fluid circulation space and a pump connectable to the fluid outlets. The pump is operable to circulate a thermal exchange fluid (e.g., a liquid such as water or an isotonic solution that inhibits the transfer of ions from the tissue) through the fluid circulation space under negative or nearly negative gauge pressure. For example, the pump normally circulates the thermal exchange fluid through the fluid circulation space at a gauge pressure between about positive 0.1 and about negative 10 pounds per square inch as measured at a fluid outlet.
Additionally, the system may further include a thermal exchange fluid reservoir connectable with the fluid inlets to supply thermal exchange fluid to the system. Thus, in practice the pump will draw thermal exchange fluid from the reservoir through the fluid inlet and into the fluid circulation space, allowing the thermal exchange fluid to directly contact the tissue region of interest. To heat the tissue region of interest, the thermal exchange fluid should be capable of releasing heat to the tissue region of interest. To cool the tissue region of interest, the thermal exchange fluid should be capable of absorbing heat from the tissue region of interest.
According to yet another aspect of the present invention, a method for local exchange of thermal energy with a tissue region of interest includes the step of covering the tissue region of interest with a flexible membrane to define a fluid circulation space between the tissue region of interest and the interior side of the flexible membrane. The method further includes the steps of interconnecting a fluid inlet to the fluid circulation space with a reservoir for fluid flow therebetween and coupling a fluid outlet from the fluid circulation space with a pump for fluid flow therebetween. The pump is operated to draw thermal exchange fluid from the reservoir through the fluid circulation space for heat transfer between the fluid and the tissue region of interest. In this regard, the fluid may be drawn by the pump through the fluid circulation space at negative or nearly negative gauge pressure (e.g., between about 0.1 psi and about xe2x88x9210.0 psi). The efficiency of the heat transfer may be further optimized by drawing the thermal exchange fluid through the fluid circulation space at a high flow rate. For example, the thermal exchange fluid may be circulated at a flow rate of between about 0.3 liters and about 4 liters per each minute for each square-meter of surface area covered by the flexible membrane (i.e. between about 0.3 liters/min-m2 and about 4 liters/min-m2).
The method may also include the step of sealing a periphery of the flexible membrane to a periphery of the tissue region of interest. In this regard, a sealable edge on the periphery of the flexible membrane is positionable on the periphery of the tissue region of interest. When the pump is operated, negative or nearly negative gauge pressure is supplied to facilitate establishment of a sealed arrangement. The sealing step may also include utilizing an adhesive to aid in sealing a periphery of the flexible membrane to the periphery of the tissue region of interest or using a non-soluble, high viscosity gel to aid in sealing the periphery of the flexible membrane to the periphery of the tissue region of interest. To take advantage of the negative or nearly negative pressure and to maintain the seal between the periphery of the flexible membrane and the periphery of the tissue region of interest when the pump is not operated, the method may further include the step of maintaining the reservoir of thermal exchange fluid at a lower height than the tissue region of interest
According to a further aspect of the present invention, an apparatus for local exchange of thermal energy with a tissue region of interest includes a flexible membrane configured for covering the tissue region of interest. The apparatus also includes a spacing structure for maintaining an interior side of the flexible membrane in a spaced relation with the tissue region of interest thereby defining a fluid circulation space between the interior side of the flexible membrane and the tissue region of interest. At least one fluid inlet communicating with the fluid circulation space and at least one fluid outlet communicating with the fluid circulation space are provided through the flexible membrane. The apparatus further includes a sealable edge configured to provide a seal between a periphery of the flexible membrane and a periphery of the tissue region of interest. A thermal exchange fluid is circulatable through the fluid circulation space from the fluid inlet(s) to the fluid outlet(s) at a predetermined gauge pressure which does not break the seal between the periphery of the flexible membrane and the periphery of the tissue region of interest. In this regard, the thermal exchange fluid may be circulated at a negative or nearly negative gauge pressure (e.g., between about 0.1 psi and xe2x88x9210.0 psi).
According to one more aspect of the present invention, a method for local exchange of thermal energy with a tissue region of interest includes the step of covering the tissue region of interest with a flexible membrane to define a fluid circulation space between the tissue region of interest and an interior side of the flexible membrane. A seal between a sealable edge of the flexible membrane and the periphery of the tissue region of interest is then established by achieving a predetermined gauge pressure within the fluid circulation space (e.g., between about 0.1 psi and xe2x88x9210.0 psi). A thermal exchange fluid is then circulated through the fluid circulation space in direct contact with the tissue region of interest for exchanging thermal energy therewith. The thermal exchange fluid is circulated through fluid circulation space at the predetermined gauge pressure to maintain the seal between the sealable edge and the periphery of the tissue region of interest.
These and other aspects of the present invention should become apparent from a review of the following detailed description when taken in conjunction with the accompanying figures.